CVE-2026-47842: Spring Security AES Encryption Vulnerability

CVE-2026-47842 is an information disclosure vulnerability in Spring Security affecting AesBytesEncryptor implementations using null initialization vectors. This weakness compromises data confidentiality in encrypted communications. This article covers technical details, affected versions from 5.7.0 to 7.1.0, impact analysis, and mitigation strategies.

CVE-2026-47842 Overview

CVE-2026-47842 affects Spring Security's AesBytesEncryptor class. Applications that instantiate the encryptor using the two-argument constructor, or that pass a null initialization vector (IV) generator while selecting Cipher Block Chaining (CBC) mode, encrypt data with an all-zero IV. A static IV in CBC mode breaks the semantic security guarantees of the algorithm and enables cryptographic attacks against ciphertext confidentiality.

Critical Impact
Data encrypted with the affected AesBytesEncryptor configurations is protected by AES/CBC with a null IV, allowing equal plaintexts to produce equal ciphertexts and exposing patterns in stored or transmitted secrets.

Affected Products

Spring Security 7.1.0
Spring Security 7.0.0 through 7.0.6, and 6.5.0 through 6.5.11
Spring Security 6.4.0 through 6.4.18, 5.8.0 through 5.8.27, and 5.7.0 through 5.7.25

Discovery Timeline

2026-08-26 - CVE-2026-47842 published to the National Vulnerability Database
2026-08-26 - Last updated in NVD database

Technical Details for CVE-2026-47842

Vulnerability Analysis

The flaw is a weak cryptography defect in Spring Security's symmetric encryption helper. AesBytesEncryptor supports multiple cipher modes, including CBC and Galois/Counter Mode (GCM). When callers construct the encryptor without supplying a BytesKeyGenerator for the IV, the class does not generate a fresh random IV per encryption operation. Instead, it produces ciphertext under AES/CBC using an all-zero IV.

CBC mode requires a unique, unpredictable IV for each encryption to prevent deterministic output. With a static IV, identical plaintexts under the same key yield identical ciphertexts. This enables an attacker with access to ciphertext to correlate encrypted values, detect repeated secrets, and mount chosen-plaintext distinguishing attacks. The vulnerability is classified as Weak Encryption and maps to [CWE-329] Generation of Predictable IV with CBC Mode.

Root Cause

The defect resides in the two-argument constructor path of AesBytesEncryptor and in the code path where a null IV generator is passed alongside CipherAlgorithm.CBC. In these cases, the encryptor omits IV randomization and defaults to an all-zero IV block. Developers who follow documented constructor signatures without explicitly wiring a secure IV source inherit the flaw silently.

Attack Vector

An attacker with authenticated network access, or with read access to ciphertext produced by the affected code, can analyze repeated ciphertext blocks to infer plaintext patterns. The attack does not require user interaction. Exploitation targets confidentiality of encrypted tokens, credentials, or persisted secrets. Integrity and availability are not directly affected. Refer to the Spring Security CVE-2026-47842 advisory for vendor-supplied technical detail.

Detection Methods for CVE-2026-47842

Indicators of Compromise

Ciphertext records in application databases where identical plaintext values produce byte-identical ciphertext output.
Application dependency manifests referencing spring-security-crypto at any affected version range.
Source code invocations of new AesBytesEncryptor(password, salt) or constructors passing null as the IV generator with CipherAlgorithm.CBC.

Detection Strategies

Perform software composition analysis (SCA) across Java build artifacts to enumerate Spring Security versions and flag matches against the vulnerable ranges.
Grep source repositories for AesBytesEncryptor instantiations and audit each call site for explicit IV generator configuration.
Review cryptographic inventories to identify systems using CBC mode without documented per-record IVs.

Monitoring Recommendations

Track cryptographic library upgrades through change management and confirm redeployment of applications after patching.
Monitor data stores for duplicate ciphertext values indicating deterministic encryption in production.
Alert on runtime loading of vulnerable spring-security-crypto versions using endpoint telemetry from your EDR platform.

How to Mitigate CVE-2026-47842

Immediate Actions Required

Upgrade spring-security-crypto to a fixed release published by the Spring Security team as identified in the vendor advisory.
Replace the two-argument AesBytesEncryptor constructor with a variant that accepts a secure BytesKeyGenerator for IV generation, or use GCM mode.
Re-encrypt any previously stored data that was protected with the affected configuration under a new key and a properly randomized IV.

Patch Information

Spring Security has published fixes referenced in the Spring Security CVE-2026-47842 advisory. Consult the advisory for the specific patched versions in the 7.0.x, 6.5.x, 6.4.x, 5.8.x, and 5.7.x branches, and apply the closest maintained release for your deployment.

Workarounds

Configure AesBytesEncryptor with an explicit IV generator, for example KeyGenerators.secureRandom(16), instead of relying on default constructors.
Migrate encryption to AES/GCM by using AesBytesEncryptor.CipherAlgorithm.GCM, which enforces IV handling suitable for authenticated encryption.
Restrict access to ciphertext at rest and in transit to reduce exposure while patching is in progress.

bash

# Example Maven dependency pin after upgrade
mvn dependency:tree | grep spring-security-crypto
# Update pom.xml to the patched version from the Spring advisory, then rebuild
mvn -U clean verify